Positive electrode material and battery containing the same

ABSTRACT

A positive electrode material contains a positive electrode active material and a first solid electrolyte material. The first solid electrolyte material is represented by Chemical Formula (1): LiαMβXγ. In Chemical Formula (1), α, β, and γ each represent a value larger than 0, M represents at least one element selected from the group consisting of metal elements other than lithium and of metalloid elements, and X represents at least one element selected from the group consisting of fluorine, chlorine, bromine, and iodine. The ratio of the volume of the positive electrode active material to the sum of the volume of the positive electrode active material and the volume of the solid electrolyte material is not less than 0.55 and not more than 0.85.

BACKGROUND 1. Technical Field

The present disclosure relates to a positive electrode material and abattery containing the positive electrode material.

2. Description of the Related Art

International Publication No. 2018/025582 discloses an all-solid-statebattery containing a halide solid electrolyte.

SUMMARY

One non-limiting and exemplary embodiment provides a battery having highdischarge capacity.

In one general aspect, the techniques disclosed here feature a positiveelectrode material containing a positive electrode active material and afirst solid electrolyte material. The first solid electrolyte materialis represented by Chemical Formula (1): Li_(α)M_(β)X_(γ). In ChemicalFormula (1), α, β, and γ each represent a value larger than 0, Mrepresents at least one element selected from the group consisting ofmetal elements other than lithium and of metalloid elements, and Xrepresents at least one element selected from the group consisting offluorine, chlorine, bromine, and iodine. The ratio of the volume of thepositive electrode active material to the sum of the volume of thepositive electrode active material and the volume of the solidelectrolyte material is not less than 0.55 and not more than 0.85.

The present disclosure provides a battery having high dischargecapacity.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating the discharge capacity of secondarybatteries of the inventive examples 1 to 11 and the comparative examples1 and 2 with respect to each volume ratio of an active material in thepositive electrode of the second batteries; and

FIG. 2 is a sectional view of a battery according to a secondembodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereafter, embodiments of the present disclosure will be described withreference to the drawings.

First Embodiment

A positive electrode material according to a first embodiment contains apositive electrode active material and a first solid electrolytematerial.

The first solid electrolyte material is a material represented byChemical Formula (1) below:

Li_(α)M_(β)X_(γ)  (1)

wherein α, β, and γ each represent a value larger than 0; M representsat least one element selected from the group consisting of metalelements other than lithium and of metalloid elements; and X representsat least one element selected from the group consisting of fluorine,chlorine, bromine, and iodine.

The ratio of the volume of the positive electrode active material to thesum of the volume of the positive electrode active material and thevolume of the first solid electrolyte material is not less than 0.55 andnot more than 0.85.

The positive electrode material according to the first embodiment iscapable of improving the discharge capacity of a battery.

International Publication No. 2018/025582 discloses a battery containinga halide solid electrolyte. However, the literature does not mention thevolume ratio of the halide solid electrolyte to the positive electrodeactive material in the positive electrode. In general, as the volumeproportion of an active material contained in a positive electrodeincreases, active material particles come into contact with each othermore easily, thereby improving electronic conductivity. As a result, theinternal resistance of the battery is decreased, thereby improving thedischarge capacity of the battery. Thus, as the volume ratio of anactive material in a positive electrode increases, the dischargecapacity of a battery is also anticipated to be improved.

As a result of studies, the inventors found that by adjusting the volumeratio of the positive electrode active material to the first solidelectrolyte material (i.e., an example of a halide solid electrolyte) inthe positive electrode as described above, the internal resistance of abattery is decreased and the discharge capacity of the battery isimproved.

In the positive electrode, when the ratio of the volume of the positiveelectrode active material to the sum of the volume of the positiveelectrode active material and the volume of the first solid electrolytematerial is less than 0.55, the battery has insufficient dischargecapacity.

Because a halide solid electrolyte has high adhesion to the positiveelectrode active material, the surface of the positive electrode activematerial tends to be covered with the first solid electrolyte materialhaving extremely small electronic conductivity. Thus, positive electrodeactive material particles are kept from being in contact with eachother, thereby increasing the internal resistance of the battery.

In the positive electrode, when the ratio of the volume of the positiveelectrode active material to the sum of the volume of the positiveelectrode active material and the volume of the first solid electrolytematerial is more than 0.85, the battery has insufficient dischargecapacity.

Because the first solid electrolyte material is hard and less prone todeformation, the contact area between the first solid electrolytematerial and the positive electrode active material can be small.Furthermore, because the volume proportion of the first solidelectrolyte material in the positive electrode decreases, ionicconductivity is decreased. Because the decrease in ionic conductivitydue to the increase in the positive electrode active material becomesmore evident than the improvement in electronic conductivity due to thesame factor, the internal resistance of the battery is expected to beincreased. Here, “deformation” refers to elastic deformation or plasticdeformation.

Examples of a solid electrolyte material include not only halide solidelectrolytes such as the first solid electrolyte material, but alsosulfide solid electrolytes and oxide solid electrolytes. Softness andadhesion to the positive electrode active material differ among solidelectrolyte materials depending on the materials thereof.

A sulfide solid electrolyte and an oxide solid electrolyte have loweradhesion to the positive electrode active material than a halide solidelectrolyte and are thus less likely to keep positive electrode activematerial particles from being in contact with each other. Furthermore, asulfide solid electrolyte is softer than a halide solid electrolyte.Because sufficient contact areas between sulfide solid electrolyteparticles and the positive electrode active material particles andbetween the sulfide solid electrolyte particles are thus provided, ionicconductivity is less likely to be decreased.

In the case where the positive electrode contains a halide solidelectrolyte, when the volume ratio of the positive electrode activematerial to the halide solid electrolyte is adjusted as described above,sufficient contact areas between positive electrode active materialparticles, between halide solid electrolyte particles, and between thepositive electrode active material particles and the halide solidelectrolyte particles are expected to be provided.

To further increase the discharge capacity of the battery, in thepositive electrode material, the ratio of the volume of the positiveelectrode active material Vpa to the sum of the volume of the positiveelectrode active material Vpa and the volume of the first solidelectrolyte material Vpe may be not less than 0.60 and not more than0.72, preferably not less than 0.65 and not more than 0.72. That is,0.60≤Vpa/(Vpa+Vpe)≤0.72 or 0.65≤Vpa/(Vpa+Vpe)≤0.72 may be satisfied.

In the present disclosure, the term “metalloid elements” refers to B,Si, Ge, As, Sb, and Te.

In the present disclosure, the term “metal elements” refers to: (i) allthe group 1 to group 12 elements (other than hydrogen) of the periodictable; and (ii) all the group 13 to group 16 elements (other than B, Si,Ge, As, Sb, Te, C, N, P, O, S, and Se) of the periodic table.

To improve the ionic conductivity of the first solid electrolytematerial, in Chemical Formula (1), M may include yttrium (Y). That is,the first solid electrolyte material may contain Y as a metal element.As a result of the improvement in the ionic conductivity, the internalresistance of the battery can be decreased and the discharge capacity ofthe battery can be improved.

The first solid electrolyte material containing Y may be, for example, acompound represented by the chemical formula Li_(a)Me_(b)Y_(c)X₆, forwhich a+mb+3c=6 and c>0 are satisfied. Here, Me represents at least oneelement selected from the group consisting of metal elements other thanLi and Y and of metalloid elements, and m represents the valence of Me.

Furthermore, Me may be at least one element selected from the groupconsisting of Mg, Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Zr, Hf, Ti, Sn, Ta,and Nb.

To improve the ionic conductivity of the first solid electrolytematerial, in Chemical Formula (1), M may include zirconium (Zr). Thatis, the first solid electrolyte material may contain Zr as a metalelement. As a result of the improvement in the ionic conductivity, theinternal resistance of the battery can be decreased and the dischargecapacity of the battery can be improved.

The first solid electrolyte material containing Zr may be, for example,a compound represented by the chemical formula Li_(p)Me′_(q)Zr_(r)X₆,for which p+m′q+4r=6 and c>0 are satisfied. Here, Me′ represents atleast one element selected from the group consisting of metal elementsother than Li, Y, and Zr and of metalloid elements, and m′ representsthe valence of Me′.

Furthermore, Me′ may be at least one element selected from the groupconsisting of Mg, Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Hf, Ti, Sn, Ta, andNb.

To improve the ionic conductivity of the first solid electrolytematerial, in Chemical Formula (1), 2.5≤α≤3, β=1, and γ=6 may besatisfied. As a result of the improvement in the ionic conductivity, thebattery can have high discharge capacity.

To improve the potential stability of the first solid electrolytematerial and the discharge capacity of the battery, in Chemical Formula(1), X may include chlorine (Cl).

To improve the ionic conductivity of the first solid electrolytematerial, in Chemical Formula (1), X may include bromine (Br).

To improve the ionic conductivity of the first solid electrolytematerial, in Chemical Formula (1), X may include iodine (I).

The first solid electrolyte material may be a material represented byChemical Formula (A1) below:

Li_(6-3d)Y_(d)X₆  (A1)

wherein X represents two or more elements selected from the groupconsisting of F, Cl, Br, and I; and 0<d<2 is satisfied.

The material represented by Chemical Formula (A1) has high ionicconductivity, which helps to further improve the discharge capacity ofthe battery.

The first solid electrolyte material may be a material represented byChemical Formula (A2) below:

Li_(3-3δ)Y_(1+δ)Cl₆  (A2)

wherein 0<δ≤0.15 is satisfied.

The material represented by Chemical Formula (A2) has high ionicconductivity, which helps to further improve the discharge capacity ofthe battery.

The first solid electrolyte material may be a material represented byChemical Formula (A3) below:

Li_(3-3δ)Y_(1+δ)Br₆  (A3)

wherein 0<γ≤0.25 is satisfied.

The material represented by Chemical Formula (A3) has high ionicconductivity, which helps to further improve the discharge capacity ofthe battery.

The first solid electrolyte material may be a material represented byChemical Formula (A4) below:

Li_(3-3δ+a)Y_(1+δ-a)Me_(a)Cl_(6-x-y)Br_(x)I_(y)  (A4)

wherein Me represents at least one element selected from the groupconsisting of Mg, Ca, Sr, Ba, and Zn; and

−1<δ<2,

0<a<3,

0<(3−3δ+a),

0<(1+δ−a),

0≤x≤6,

0≤y≤6, and

(x+y)≤6

are satisfied.

The material represented by Chemical Formula (A4) has high ionicconductivity, which helps to further improve the discharge capacity ofthe battery.

The first solid electrolyte material may be a material represented byChemical Formula (A5) below:

Li_(3-3δ)Y_(1+δ-a)Me_(a)Cl_(6-x-y)Br_(x)I_(y)  (A5)

wherein Me represents at least one element selected from the groupconsisting of Al, Sc, Ga, and Bi; and

−1<δ<1,

0<a<2,

0<(1+δ−a),

0≤x≤6,

0≤y≤6, and

(x+y)≤6

are satisfied.

The material represented by Chemical Formula (A5) has high ionicconductivity, which helps to further improve the discharge capacity ofthe battery.

The first solid electrolyte material may be a material represented byChemical Formula (A6) below:

Li_(3-3δ-a)Y_(1+6-a)Me_(a)Cl_(6-x-y)Br_(x)I_(y)  (A6)

wherein Me represents at least one element selected from the groupconsisting of Zr, Hf, and Ti; and

−1<δ<1,

0<a<1.5,

0<(3−3δ−a),

0<(1+δ−a),

0≤x≤6,

0≤y≤6, and

(x+y)≤6

are satisfied.

The material represented by Chemical Formula (A6) has high ionicconductivity, which helps to further improve the discharge capacity ofthe battery.

The first solid electrolyte material may be a material represented byChemical Formula (A7) below:

Li_(3-3δ-2a)Y_(1+δ-a)Me_(a)Cl_(6-x-y)Br_(x)I_(y)  (A7)

wherein Me represents at least one element selected from the groupconsisting of Ta and Nb; and

−1<δ<1,

0<a<1.2,

0<(3−3δ−2a),

0<(1+δ−a),

0≤x≤6,

0≤y≤6, and

(x+y)≤6

are satisfied.

The material represented by Chemical Formula (A7) has high ionicconductivity, which helps to further improve the discharge capacity ofthe battery.

As the first solid electrolyte material, for example, Li₃YX₆, Li₂MgX₄,Li₂FeX₄, Li(Al,Ga,In)X₄, or Li₃(Al,Ga,In)X₆ may be used. As used herein,“(Al,Ga,In)” refers to at least one element selected from the groupconsisting of A1, Ga, and In.

The positive electrode active material is a material capable of storingand releasing metal ions (e.g., lithium ions).

Examples of the positive electrode active material include lithiumtransition metal oxides (e.g., Li(NiCoAl)O₂, Li(NiCoMn)O₂, and LiCoO₂),transition metal fluorides, polyanions, fluoride polyanion materials,transition metal sulfides, transition metal oxysulfides, and transitionmetal oxynitrides. When a lithium transition metal oxide is used as thepositive electrode active material, the manufacturing costs can bedecreased and the average discharge voltage of the battery can beimproved.

To improve the discharge capacity and energy density of the battery, thepositive electrode active material may be a lithium nickel manganesecobalt oxide. The lithium nickel manganese cobalt oxide may beLi(NiCoMn)O₂.

To improve the discharge capacity and energy density of the battery, thepositive electrode active material may be a lithium nickel cobaltaluminum oxide. The lithium nickel cobalt aluminum oxide may beLi(NiCoAl)O₂.

To improve the charge-discharge efficiency of the battery, at least aportion of the surface of the positive electrode active material may becoated with a coating material.

A material having low electronic conductivity can be used as the coatingmaterial. Examples of the coating material include oxide materials andoxide solid electrolyte materials.

Examples of the oxide materials include SiO₂, Al₂O₃, TiO₂, B₂O₃, Nb₂O₅,WO₃, and ZrO₂. Examples of the oxide solid electrolyte materials includeLi—Nb—O compounds such as LiNbO₃, Li—B—O compounds such as LiBO₂ andLi₃BO₃, Li—Al—O compounds such as LiAlO₂, Li—Si—O compounds such asLi₄SiO₄, Li—S—O compounds such as Li₂SO₄, Li—Ti—O compounds such asLi₄Ti₅O₁₂, Li—Zr—O compounds such as Li₂ZrO₃, Li—Mo—O compounds such asLi₂MoO₃, Li-V-O compounds such as LiV₂O₅, and Li—W—O compounds such asLi₂WO₄.

In view of ionic conductivity and potential stability, the coatingmaterial may be an oxide solid electrolyte. By using an oxide solidelectrolyte for the coating material, the charge-discharge efficiency ofthe battery can further be improved.

The oxide solid electrolyte material used as the coating material may belithium niobate (LiNbO₃). Lithium niobate has high ionic conductivityand high potential stability.

When the surface of the positive electrode active material is coatedwith the coating material, the positive electrode active material andthe first solid electrolyte material are interposed by the coatingmaterial and do not come into contact with each other. A coating layercontaining the coating material may have a thickness of not less than 1nm and not more than 100 nm. When the coating layer has a thickness ofnot less than 1 nm, the positive electrode active material and the firstsolid electrolyte material are suppressed from being in contact witheach other, which helps to suppress a side reaction of the first solidelectrolyte material. As a result, the charge-discharge efficiency ofthe battery can be improved. When the coating layer has a thickness ofnot more than 100 nm, the internal resistance of the battery can besufficiently small. Thus, the discharge capacity of the battery can beimproved.

To improve the output of the battery, a portion of the surface of thepositive electrode active material may be coated. As a result ofpositive electrode active material particles coming in contact with eachother via a portion without the coating layer, the electronicconductivity between the positive electrode active material particlesare improved.

To improve the charge-discharge efficiency of the battery, the entiresurface of the positive electrode active material may be coated with thecoating material. As a result of the positive electrode active materialand the first solid electrolyte material being suppressed from being incontact with each other, a side reaction of the first solid electrolytematerial can be suppressed.

The form of the first solid electrolyte material is not limited. Thefirst solid electrolyte material may be in the form of, for example, aneedle, a sphere, or an ellipsoid. The first solid electrolyte materialmay also be in the form of particles.

When the first solid electrolyte material is in the form of particles(e.g., spherical particles), first solid electrolyte particles may havea median diameter of not more than 100 μm, preferably not more than 10μm, in which case the positive electrode active material and the firstsolid electrolyte particles can be well dispersed in the positiveelectrode material. As a result, the charge-discharge characteristics ofthe battery can be improved.

The first solid electrolyte particles may have a median diameter smallerthan the median diameter of the positive electrode active material, inwhich case the first solid electrolyte particles and the positiveelectrode active material can be well dispersed in the positiveelectrode material. As a result, the charge-discharge characteristics ofthe battery can be improved.

The positive electrode active material may have a median diameter of notless than 0.1 μm and not more than 100 μm. When the positive electrodeactive material has a median diameter of not less than 0.1 μm, thepositive electrode active material and the first solid electrolyteparticles can be well dispersed in the positive electrode material. As aresult, the charge-discharge characteristics of the battery can beimproved. When the positive electrode active material has a mediandiameter of not more than 100 μm, the diffusion rate of lithium in thepositive electrode active material is improved. Thus, the battery canoperate with a high output.

(Method for Manufacturing First Solid Electrolyte Material)

The first solid electrolyte material according to the first embodimentcan be manufactured, for example, through the following method.

Halide raw material powders are prepared considering the composition ofthe product. For example, when Li₃YCl₆ is produced, LiCl and YCl₃ areprepared in a molar ratio of 3:1.

The elements represented by M, Me, Me′, and X in the above-describedchemical formulas are determined by selecting the kind of raw materialpowders. The values represented by α, β, γ, a, b, c, and d aredetermined by adjusting the raw material powders, the combination ratiothereof, and the synthesis process therefor.

Raw material powders are mixed to obtain a mixed powder. Particles ofthe mixed powder are caused to mechanochemically (i.e., through a methodof mechanochemical milling treatment) react with each other in a mixingapparatus such as a planetary ball mill to obtain a reactant. Thereactant may be fired in a vacuum or an inert atmosphere. Alternatively,the mixed powder may be fired in a vacuum or an inert atmosphere toobtain a reactant.

The first solid electrolyte material can be obtained through theabove-described method.

Second Embodiment

Hereafter, a second embodiment will be described. Descriptionsoverlapping those of the first embodiment will be omitted whereappropriate.

A battery according to the second embodiment includes a positiveelectrode, a negative electrode, and an electrolyte layer. The positiveelectrode contains the positive electrode material according to thefirst embodiment. The electrolyte layer is disposed between the positiveelectrode and the negative electrode. The electrolyte layer contains asecond solid electrolyte material. The battery according to the secondembodiment has high discharge capacity.

FIG. 2 is a sectional view of a battery 1000 according to the secondembodiment. The battery 1000 includes a positive electrode 101, anelectrolyte layer 102, and a negative electrode 103. The positiveelectrode 101 includes a first solid electrolyte particle 110 and apositive electrode active material particle 111. The electrolyte layer102 is disposed between the positive electrode 101 and the negativeelectrode 103. The electrolyte layer 102 contains the second solidelectrolyte material.

In view of the energy density and output of the battery, the positiveelectrode 101 may have a thickness of not less than 10 μm and not morethan 500 μm.

To improve the discharge capacity of the battery, the second solidelectrolyte material may be a halide solid electrolyte.

The halide solid electrolyte may be a compound exemplified as the firstsolid electrolyte material in the first embodiment. The second solidelectrolyte material may be a material that is the same as or differentfrom the first solid electrolyte material.

The second solid electrolyte material may be a sulfide solidelectrolyte. The use of a sulfide solid electrolyte having goodreduction stability enables the use of a low-potential negativeelectrode material. As a result, the energy density of the battery canbe improved.

Examples of the sulfide solid electrolyte include Li₂S—P₂S₅, Li₂S—SiS₂,Li₂S—B₂S₃, Li₂S—GeS₂, Li_(3.25)Ge_(0.25)P_(0.75)S₄, and Li₁₀GeP₂S₁₂.Furthermore, LiX, Li₂O, MO, or Li_(p)MO_(q) may be added to theforegoing. Here, M represents at least one element selected from thegroup consisting of P, Si, Ge, B, Al, Ga, In, Fe, and Zn, p and q eachrepresent a natural number, and X represents at least one elementselected from the group consisting of F, Cl, Br, and I.

The second solid electrolyte material may be an oxide solid electrolyte.

Examples of the oxide solid electrolyte include: (i) NASICON solidelectrolytes such as LiTi₂(PO₄)₃ and its element-substitutedderivatives; (ii) (LaLi)TiO₃-based perovskite solid electrolytes; (iii)LISICON solid electrolytes such as Li₁₄ZnGe₄O₁₆, Li₄SiO₄, LiGeO₄, andtheir element-substituted derivatives; (iv) garnet solid electrolytessuch as Li₇La₃Zr₂O₁₂ and its element-substituted derivatives; (v) Li₃PO₄and its N-substituted derivatives; and (vi) glass or glass ceramicsformed by adding Li₂SO₄ or Li₂CO₃ to a Li—B—O compound such as LiBO₂ orLi₃BO₃.

The second solid electrolyte material may be a polymer solidelectrolyte.

Examples of the polymer solid electrolyte include polymer compounds andlithium salt compounds. The polymer compounds may have an ethylene oxidestructure. A polymer solid electrolyte having an ethylene oxidestructure is capable of containing a large amount of lithium salt, whichhelps to further improve ionic conductivity.

Examples of the lithium salt include LiPF₆, LiBF₄, LiSbF₆, LiAsF₆,LiSO₃CF₃, LiN(SO₂CF₃)₂, LiN(SO₂C₂F₅)₂, LiN(SO₂CF₃)(SO₂C₄F₉), andLiC(SO₂CF₃)₃. One lithium salt selected from the foregoing may be usedalone. Alternatively, mixtures of two or more lithium salts selectedfrom the foregoing may be used.

The second solid electrolyte material may be a complex hydride solidelectrolyte.

Examples of the complex hydride solid electrolyte include LiBH₄—LiI andLiBH₄—P₂S₅.

The electrolyte layer 102 may be formed of only one of or two or more ofthe materials exemplified as the second solid electrolyte material. Forexample, the electrolyte layer 102 may contain a halide solidelectrolyte material and a sulfide solid electrolyte material.

When the electrolyte layer 102 is formed of two or more materials, thematerials may be uniformly dispersed. Alternatively, a plurality oflayers each formed of a single material may be stacked in the stackingdirection of the battery.

In view of suppressing a short circuit between the positive electrode101 and the negative electrode 103 and of the output of the battery, theelectrolyte layer 102 may have a thickness of not less than 1 μm and notmore than 300 μm.

The negative electrode 103 contains a material capable of storing andreleasing metal ions (e.g., lithium ions). An example of the material isa negative electrode active material.

Examples of the negative electrode active material include metalmaterials, carbon materials, oxides, nitrides, tin compounds, andsilicon compounds. The metal materials may be elemental metals oralloys. Examples of the metal materials include lithium metal andlithium alloys. Examples of the carbon materials include naturalgraphite, coke, carbons undergoing graphitization, carbon fibers,spherical carbons, artificial graphite, and amorphous carbons. In viewof capacity density, silicon (Si), tin (Sn), a silicon compound, or atin compound may be used as a negative electrode active material.

The negative electrode 103 may contain a solid electrolyte material, inwhich case the lithium ionic conductivity in the negative electrode 103is improved. As a result, the battery can operate with a high output.The solid electrolyte material may be a material exemplified as thesecond solid electrolyte material.

The negative electrode active material may have a median diameter of notless than 0.1 μm and not more than 100 μm. When the negative electrodeactive material has a median diameter of not less than 0.1 μm, thenegative electrode active material and the solid electrolyte materialcan be well dispersed in the negative electrode 103. As a result, thecharge-discharge characteristics of the battery can be improved. Whenthe negative electrode active material has a median diameter of not morethan 100 μm, the diffusion rate of lithium in the negative electrodeactive material is improved. Thus, the battery can operate with a highoutput.

The negative electrode active material may have a median diameter largerthan the median diameter of the solid electrolyte material, in whichcase the negative electrode active material and the solid electrolytematerial can be well dispersed.

In view of the energy density and output of the battery, in the negativeelectrode 103, the ratio of the volume of the negative electrode activematerial to the sum of the volume of the negative electrode activematerial and the volume of the solid electrolyte material may be notless than 0.30 and not more than 0.95.

In view of the energy density and output of the battery, the negativeelectrode 103 may have a thickness of not less than 10 μm and not morethan 500 μm.

At least one selected from the group consisting of the positiveelectrode 101, the electrolyte layer 102, and the negative electrode 103may contain a binder to improve the adhesion between particles.

Examples of the binder include polyvinylidene fluoride,polytetrafluoroethylene, polyethylene, polypropylene, aramid resin,polyamide, polyimide, polyamide-imide, polyacrylonitrile, polyacrylicacid, methyl polyacrylate esterne, ethyl polyacrylate eter, hexylpolyacrylate ester, polymethacrylic acid, methyl polymethacrylate ester,ethyl polymethacrylate ester, hexyl polymethacrylate ester, polyvinylacetate, polyvinylpyrrolidone, polyether, polyethersulfone,hexafluoropolypropylene, styrene-butadiene rubber, and carboxymethylcellulose. Copolymers can also be used as the binder. Examples of such abinder include copolymers of two or more materials selected from thegroup consisting of tetrafluoroethylene, hexafluoroethylene,hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride,chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene,fluoromethyl vinyl ether, acrylic acid, and hexadiene.

A mixture of two or more selected from the above-described materials mayalso be used as the binder.

At least one selected from the positive electrode 101 and the negativeelectrode 103 may contain a conductive agent to improve electronicconductivity.

Examples of the conductive agent include: (i) graphites such as naturalgraphite and artificial graphite; (ii) carbon blacks such as acetyleneblack and Ketjen black; (iii) conductive fibers such as carbon fibersand metal fibers; (iv) fluorinated carbons; (v) metal powders such asaluminum powder; (vi) conductive whiskers such as zinc oxide whiskersand potassium titanate whiskers; (vii) conductive metal oxides such astitanium oxides; and (viii) conductive polymer compounds such aspolyaniline, polypyrrole, and polythiophene. To achieve low costs, theforegoing conductive agents (i) and (ii) can be used.

The form of the battery according to the second embodiment is, forexample, coin-like, cylindrical, square, sheet-like, button-like, flat,or stacked.

EXAMPLES

The present disclosure will be described in further detail withreference to Examples.

Inventive Example 1

(Production of First Solid Electrolyte Material)

In an argon atmosphere of a dew point of −60° C. or less (hereafterreferred to as a “dry argon atmosphere”), LiBr, LiCl, YCl₃, and YBr₃were prepared as raw material powders so as to have a molar ratio ofLiBr:LiCl:YCl₃:YBr₃=1:5:1:1. The mixture of the raw material powders wastreated with a planetary ball mill (P-7, manufactured by Fritsch, Inc.)for 25 hours at 600 rpm to cause the raw material powders tomechanochemically react. In this way, a powder of a first solidelectrolyte material of the inventive example 1 was obtained. The firstsolid electrolyte material of the inventive example 1 had a compositionrepresented by Li₃YBr₂Cl₄.

(Production of Positive Electrode Material)

In a dry argon atmosphere, a powder of Li(NiCoMn)O₂ (hereafter referredto as “NCM”), which is a positive electrode active material, and apowder of the first solid electrolyte material of the inventive example1 were prepared so as to have a volume ratio of 85:15. The materialswere mixed in an agate mortar. In this way, a positive electrodematerial of the inventive example 1 was obtained.

Inventive Example 2

(Production of Positive Electrode Material)

In a dry argon atmosphere, a powder of NCM and a powder of the firstsolid electrolyte material of the inventive example 1 were prepared soas to have a volume ratio of 80:20. Except for this, the same procedurewas performed as in the inventive example 1 to obtain a positiveelectrode material of the inventive example 2.

Inventive Example 3

(Production of Positive Electrode Material)

In a dry argon atmosphere, a powder of NCM and a powder of the firstsolid electrolyte material of the inventive example 1 were prepared soas to have a volume ratio of 72:28. Except for this, the same procedurewas performed as in the inventive example 1 to obtain a positiveelectrode material of the inventive example 3.

Inventive Example 4

(Production of Positive Electrode Material)

In a dry argon atmosphere, a powder of NCM and a powder of the firstsolid electrolyte material of the inventive example 1 were prepared soas to have a volume ratio of 65:35. Except for this, the same procedurewas performed as in the inventive example 1 to obtain a positiveelectrode material of the inventive example 4.

Inventive Example 5

(Production of Positive Electrode Material)

In a dry argon atmosphere, a powder of NCM and a powder of the firstsolid electrolyte material of the inventive example 1 were prepared soas to have a volume ratio of 55:45. Except for this, the same procedurewas performed as in the inventive example 1 to obtain a positiveelectrode material of the inventive example 5.

Inventive Example 6

(Production of First Solid Electrolyte Material)

In a dry argon atmosphere, LiBr, LiCl, YCl₃, and YBr₃ were prepared asraw material powders to achieve a molar ratio ofLiBr:LiCl:YCl₃:YBr₃=3:3:1:1. Except for this, the same procedure wasperformed as in the inventive example 1 to obtain a first solidelectrolyte material of the inventive example 6. The first solidelectrolyte material of the inventive example 6 had a compositionrepresented by Li₃YBr₃Cl₃.

(Production of Positive Electrode Material)

In a dry argon atmosphere, a powder of NCM and a powder of the firstsolid electrolyte material of the inventive example 6 were prepared soas to have a volume ratio of 60.6:39.4. Except for this, the sameprocedure was performed as in the inventive example 1 to obtain apositive electrode material of the inventive example 6.

Inventive Example 7

(Production of First Solid Electrolyte Material) In a dry argonatmosphere, LiCl and YCl₃ were prepared as raw material powders so as tohave a molar ratio of LiCl:YCl₃=3:1. Except for this, the same procedurewas performed as in the inventive example 1 to obtain a first solidelectrolyte material of the inventive example 7. The first solidelectrolyte material of the inventive example 7 had a compositionrepresented by Li₃YCl₆.

(Production of Positive Electrode Material)

In a dry argon atmosphere, a powder of NCM and a powder of the firstsolid electrolyte material of the inventive example 7 were prepared soas to have a volume ratio of 58.5:41.5. Except for this, the sameprocedure was performed as in the inventive example 1 to obtain apositive electrode material of the inventive example 7.

Inventive Example 8

(Production of First Solid Electrolyte Material)

In a dry argon atmosphere, LiBr and YBr₃ were prepared as raw materialpowders so as to have a molar ratio of LiBr:YBr₃=3:1. Except for this,the same procedure was performed as in the inventive example 1 to obtaina first solid electrolyte material of the inventive example 8. The firstsolid electrolyte material of the inventive example 8 had a compositionrepresented by Li₃YBr₆.

(Production of Positive Electrode Material)

In a dry argon atmosphere, a powder of NCM and a powder of the firstsolid electrolyte material of the inventive example 8 were prepared soas to have a volume ratio of 68.8:31.2. Except for this, the sameprocedure was performed as in the inventive example 1 to obtain apositive electrode material of the inventive example 8.

Inventive Example 9

(Production of First Solid Electrolyte Material)

In a dry argon atmosphere, LiCl, ZrCl₄, and YCl₃ were prepared as rawmaterial powders so as to have a molar ratio of LiCl:ZrCl₄:YCl₃=5:1:1.Except for this, the same procedure was performed as in the inventiveexample 1 to obtain a first solid electrolyte material of the inventiveexample 9. The first solid electrolyte material of the inventive example9 had a composition represented by Li_(2.5)Zr_(0.5)Y_(0.5)Cl₆.

(Production of Positive Electrode Material)

In a dry argon atmosphere, a powder of NCM and a powder of the firstsolid electrolyte material of the inventive example 9 were prepared soas to have a volume ratio of 65:35. Except for this, the same procedurewas performed as in the inventive example 1 to obtain a positiveelectrode material of the inventive example 9.

Inventive Example 10

(Production of Positive Electrode Material)

In a dry argon atmosphere, a powder of NCM and a powder of the firstsolid electrolyte material of the inventive example 9 were prepared in avolume ratio of 60:40. Except for this, the same procedure was performedas in the inventive example 1 to obtain a positive electrode material ofthe inventive example 10.

Inventive Example 11

(Production of First Solid Electrolyte Material)

In a dry argon atmosphere, LiCl and YCl₃ were prepared as raw materialpowders so as to have a molar ratio of LiCl:YCl₃=3:1. Except for this,the same procedure was performed as in the inventive example 1 to obtaina first solid electrolyte material of the inventive example 11. Thefirst solid electrolyte material of the inventive example 11 had acomposition represented by Li₃YCl₆.

(Production of Positive Electrode Material)

In a dry argon atmosphere, Li(NiCoAl)O₂ (hereafter referred to as“NCA”), which is a positive electrode active material, and the firstsolid electrolyte material of the inventive example 11 were prepared soas to have a volume ratio of 58.5:41.5. Except for this, the sameprocedure was performed as in the inventive example 1 to obtain apositive electrode material of the inventive example 11.

Comparative Example 1

(Production of Positive Electrode Material)

In a dry argon atmosphere, a powder of NCM and a powder of the firstsolid electrolyte material of the inventive example 1 were prepared soas to have a volume ratio of 90:10. Except for this, the same procedurewas performed as in the inventive example 1 to obtain a positiveelectrode material of the comparative example 1.

Comparative Example 2

(Production of Positive Electrode Material)

In a dry argon atmosphere, a powder of NCM and a powder of the firstsolid electrolyte material of the inventive example 1 were prepared soas to have a volume ratio of 50:50. Except for this, the same procedurewas performed as in the inventive example 1 to obtain a positiveelectrode material of the comparative example 2.

(Production of Sulfide Solid Electrolyte)

In a dry argon atmosphere, Li₂S and P₂S₅ were prepared to achieve amolar ratio of Li₂S:P₂S₅=75:25. The mixture of these materials wastreated with a planetary ball mill (P-7, manufactured by Fritsch, Inc.)for 10 hours at 510 rpm to cause the materials to mechanochemicallyreact. In this way, a glassy solid electrolyte was obtained. Theobtained glassy solid electrolyte was heat treated at 270° C. for 2hours in an inert atmosphere to obtain a glass-ceramic sulfide solidelectrolyte. The sulfide solid electrolyte had a composition representedby Li₂S—P₂S₅. As used herein, Li₂S—P₂S₅ used in the inventive examplesand the comparative examples is simply referred to as a “sulfide solidelectrolyte”.

(Production of Negative Electrode Material)

In a dry argon atmosphere, graphite and the sulfide solid electrolytewere prepared so as to have a mass ratio of 60:40. The materials weremixed in an agate mortar. In this way, negative electrode material wasobtained. The negative electrode material was used in the inventiveexamples 1 to 5.

(Production of Secondary Battery)

(Secondary Batteries of Inventive Examples 1 to 5 and ComparativeExamples 1 and 2)

In an insulating cylinder having an inner diameter of 9.5 mm, thesulfide solid electrolyte (40 mg) and the first solid electrolytematerial (55 mg) of the inventive example 1 were stacked in this orderto obtain a stacking structure. A pressure of 160 MPa was applied to thestacking structure to form a solid electrolyte layer.

Next, the above-described negative electrode material (15.74 mg) wasstacked on the layer formed of the sulfide solid electrolyte (of thesolid electrolyte layer), and the positive electrode material of theinventive example 1 (in an amount equivalent to 14.17 mg of the positiveelectrode active material) was stacked on the layer formed of the firstsolid electrolyte material of the inventive example 1 (of the solidelectrolyte layer) to provide a stacking structure. A pressure of 720MPa was applied to the stacking structure to form a negative electrodeand a positive electrode.

A stainless steel current collector was disposed on each of the positiveelectrode and the negative electrode, and current collecting leads wereattached to the current collectors.

Finally, the inside of the insulating cylinder was blocked from theouter atmosphere, by using an insulating ferrule, and sealed. In thisway, a secondary battery of the inventive example 1 was obtained.

The same procedure as in the production of the secondary battery of theinventive example 1 was performed to obtain secondary batteries of theinventive examples 2 to 5 and the comparative examples 1 and 2, exceptthat the positive electrode materials of the inventive examples 2 to 5and the comparative examples 1 and 2 were used in place of the positiveelectrode material of the inventive example 1.

(Secondary Battery of Inventive Example 6)

In an insulating cylinder having an inner diameter of 9.5 mm, the firstsolid electrolyte material of the inventive example 6 (80 mg) was placedand a pressure of 80 MPa was applied thereto. Subsequently, after thepositive electrode material of the inventive example 6 (in an amountequivalent to 7 mg of the positive electrode active material) was placedin the cylinder, a pressure of 360 MPa was applied to the solidelectrolyte material of the inventive example 6 and the positiveelectrode material of the inventive example 6. In this way, a solidelectrolyte layer and a positive electrode were formed.

Next, In metal foil (thickness: 200 μm), Li metal foil (thickness: 300μm), and In metal foil (thickness: 200 μm) were stacked on the solidelectrolyte layer in this order to obtain a stacking structure. Apressure of 80 MPa was applied to the stacking structure to form anegative electrode.

Except for the above matters, the same procedure as in the production ofthe secondary battery of the inventive example 1 was performed to obtaina secondary battery of the inventive example 6.

(Secondary Batteries of Inventive Examples 7 and 11)

The same procedure as in the production of the secondary battery of theinventive example 6 was performed to obtain a secondary battery of theinventive example 7,except that the positive electrode material of theinventive example 7 (in an amount equivalent to a 7 mg of the positiveelectrode active material) and the first solid electrolyte material ofthe inventive example 7 were used in place of the positive electrodematerial of the inventive example 6 and the first solid electrolytematerial of the inventive example 6.

The same procedure as in the production of the secondary battery of theinventive example 7 was performed to obtain a secondary battery of theinventive example 11, except that the positive electrode material of theinventive example 11 was used in place of the positive electrodematerial of the inventive example 7.

(Secondary Battery of Inventive Example 8)

The same procedure as in the production of the secondary battery of theinventive example 6 was performed to obtain a secondary battery of theinventive example 8,except that the positive electrode material of theinventive example 8 (in an amount equivalent to a 7 mg of the positiveelectrode active material) and the first solid electrolyte material ofthe inventive example 8 were used in place of the positive electrodematerial of the inventive example 6 and the first solid electrolytematerial of the inventive example 6.

(Secondary Batteries of Inventive Examples 9 and 10)

In an insulating cylinder having an inner diameter of 9.5 mm, thesulfide solid electrolyte (40 mg) and the first solid electrolytematerial of the inventive example 9 (40 mg) were stacked in this orderto provide a stacking structure. A pressure of 80 MPa was applied to theprovided stacking structure to form a solid electrolyte layer.

Next, the positive electrode material of the inventive example 9 (in anamount equivalent to 7 mg of the positive electrode active material) wasstacked on the layer formed of the solid electrolyte layer of theinventive example 9, to provide a stacking structure. A pressure of 360MPa was applied to the provided stacking structure to form a positiveelectrode.

Except for the above matters, the same procedure as in the production ofthe secondary battery of the inventive example 6 was performed to obtaina secondary battery of the inventive example 9.

The same procedure as in the production of the secondary battery of theinventive example 9 was performed to obtain a secondary battery of theinventive example 10,except that the positive electrode material of theinventive example 10 was used in place of the positive electrodematerial of the inventive example 9.

(Charge-Discharge Test)

(Secondary Batteries of Inventive Examples 1 to 5 and ComparativeExamples 1 and 2)

Each obtained secondary battery was disposed in a thermostatic chambermaintained at 25° C.

Each secondary battery was charged until the voltage reached 4.2 V at acurrent value of 142 μA equivalent to a 0.05 C (20-hour) rate.

Next, each secondary battery was discharged until the voltage reached2.5 V likewise at a current value of 142 μA equivalent to a 0.05 C rate.

(Secondary Batteries of Inventive Examples 6 to 11)

Each obtained secondary battery was disposed in a thermostatic chambermaintained at 25° C.

Each secondary battery was charged until the voltage reached 3.7 V at acurrent value of 70 μA equivalent to a 0.05 C (20-hour) rate.

Next, each secondary battery was discharged until the voltage reached1.9 V likewise at a current value of 70 μA equivalent to a 0.05 C rate.

The measurement results of the discharge capacity of the secondarybatteries of the inventive examples 1 to 11 and the comparative examples1 and 2 are presented in FIG. 1 and Table 1. The expression “volumeratio of active material in positive electrode” in FIG. 1 and Table 1refers to the ratio of the volume of the positive electrode activematerial to the sum of the volume of the positive electrode activematerial and the volume of the solid electrolyte material in thepositive electrode.

In FIG. 1, a dotted line is drawn across the plots corresponding to theinventive examples 1 and 5 and the comparative examples 1 and 2.

TABLE 1 Volume ratio Positive of active Second Negative Dis- electrodeFirst solid material solid electrode charge active electrolyte inpositive electrolyte active capacity material material electrodematerial material [mAh/g] Inventive NCM Li₃YBr₂Cl₄ 0.85 Sulfide solidGraphite 171.1 example 1 electrolyte Inventive NCM Li₃YBr₂Cl₄ 0.80Sulfide solid Graphite 169.5 example 2 electrolyte Inventive NCMLi₃YBr₂Cl₄ 0.72 Sulfide solid Graphite 173.2 example 3 electrolyteInventive NCM Li₃YBr₂Cl₄ 0.65 Sulfide solid Graphite 179.2 example 4electrolyte Inventive NCM Li₃YBr₂Cl₄ 0.55 Sulfide solid Graphite 172.6example 5 electrolyte Inventive NCM Li₃YBr₃Cl₃ 0.606 Li₃YBr₃Cl₃ In-Li170.3 example 6 alloy Inventive NCM Li₃YCl₆ 0.585 Li₃YCl₆ In-Li 167.2example 7 alloy Inventive NCM Li₃YBr₆ 0.688 Li₃YBr₆ In-Li 178.4 example8 alloy Inventive NCM Li_(2.5)Zr_(0.5) 0.65 Sulfide solid In-Li 177.6example 9 Y_(0.5)Cl₆ electrolyte alloy Inventive NCM Li_(2.5)Zr_(0.5)0.60 Sulfide solid In-Li 177.9 example 10 Y_(0.5)Cl₆ electrolyte alloyInventive NCA Li₃YCl₆ 0.585 Li₃YCl₆ In-Li 173.1 example 11 alloyComparative NCM Li₃YBr₂Cl₄ 0.90 Sulfide solid Graphite 130.2 example 1electrolyte Comparative NCM Li₃YBr₂Cl₄ 0.50 Sulfide solid Graphite 102.0example 2 electrolyte

DISCUSSION

As evident in Table 1, the batteries containing the positive electrodematerials of the inventive examples 1 to 11 have high dischargecapacity.

As evident in a comparison of the comparative examples 1 and 2 to theinventive examples 1 to 5, if the ratio of the volume of the positiveelectrode active material to the sum of the volume of the positiveelectrode active material and the volume of the solid electrolytematerial in the positive electrode is out of the range of not less than0.55 and not more than 0.85, the discharge capacity of the batteries islargely decreased.

As evident in a comparison of the inventive examples 3 and 4 with theinventive examples 1, 2 and 5, if the ratio of the volume of thepositive electrode active material to the sum of the volume of thepositive electrode active material and the volume of the solidelectrolyte material in the positive electrode is in the range of notless than 0.65 and not more than 0.72, the batteries have higherdischarge capacity.

As described above, the positive electrode material according to thepresent disclosure is suitable for providing a battery having highdischarge capacity.

INDUSTRIAL APPLICABILITY

The positive electrode material and the battery according to the presentdisclosure are to be applied to, for example, all-solid-state lithiumion secondary batteries.

1. A positive electrode material comprising: a positive electrode activematerial; and a first solid electrolyte material, wherein the firstsolid electrolyte material is represented by the following chemicalformula (1) below:Li_(α)M_(β)X_(γ)  (1) where α, β, and γ each represent a value largerthan 0; M represents at least one element selected from the groupconsisting of metal elements other than lithium and of metalloidelements; and X represents at least one element selected from the groupconsisting of fluorine, chlorine, bromine, and iodine, and a ratio of avolume of the positive electrode active material to a sum of the volumeof the positive electrode active material and a volume of the firstsolid electrolyte material is not less than 0.55 and not more than 0.85.2. The positive electrode material according to claim 1, wherein theratio is not less than 0.60 and not more than 0.72.
 3. The positiveelectrode material according to claim 2, wherein the ratio is not lessthan 0.65 and not more than 0.72.
 4. The positive electrode materialaccording to claim 1, wherein M includes yttrium.
 5. The positiveelectrode material according to claim 1, wherein M includes zirconium.6. The positive electrode material according to claim 1, wherein inChemical Formula (1), 2.5≤α≤3, β=1, and γ=6 are satisfied.
 7. Thepositive electrode material according to claim 1, wherein X includeschlorine.
 8. The positive electrode material according to claim 1,wherein X includes bromine.
 9. The positive electrode material accordingto claim 1, wherein the positive electrode active material is a lithiumnickel manganese cobalt oxide.
 10. The positive electrode materialaccording to claim 1, wherein the positive electrode active material isa lithium nickel cobalt aluminum oxide.
 11. A battery comprising: apositive electrode that contains the positive electrode materialaccording to claim 1; a negative electrode; and an electrolyte layerthat is disposed between the positive electrode and the negativeelectrode and that contains a second solid electrolyte material.
 12. Thebattery according to claim 11, wherein the second solid electrolytematerial is a halide solid electrolyte.
 13. The battery according toclaim 12, wherein the second solid electrolyte material is a materialthat is the same as the first solid electrolyte material.
 14. Thebattery according to claim 11, wherein the second solid electrolytematerial is a sulfide solid electrolyte.